Water in Atmosphere- 2 | Geography for UPSC 2024 (Pre & Mains) PDF Download

 Page 1


 
WATER IN THE ATMOSPHERE – PART - 2 
FORMS OF CONDENSATION 
The forms of condensation can be classified on the basis of temperature at 
which the dew point is reached. 
Condensation can take place when the dew point is 
? lower than the freezing point, 
? higher than the freezing point. 
White frost, snow and some clouds (cirrus clouds) are produced when the 
temperature is lower than the freezing point. 
Dew, fog and clouds result even when the temperature is higher than the 
freezing point. 
NOTE: 
Forms of condensation may also be classified on the basis of their location, 
i.e. at or near the earth’s surface and in free air. 
Dew, white frost, fog and mist come in the first category, whereas clouds 
are in the second category. 
 
DEW 
 
 When the moisture is deposited in the form of water droplets on cooler 
surfaces of solid objects such as stones, grass blades and plant leaves, it is 
known as dew.  
At night, various objects such as leaves etc. may frequently become cooler 
that the air above it.  
Page 2


 
WATER IN THE ATMOSPHERE – PART - 2 
FORMS OF CONDENSATION 
The forms of condensation can be classified on the basis of temperature at 
which the dew point is reached. 
Condensation can take place when the dew point is 
? lower than the freezing point, 
? higher than the freezing point. 
White frost, snow and some clouds (cirrus clouds) are produced when the 
temperature is lower than the freezing point. 
Dew, fog and clouds result even when the temperature is higher than the 
freezing point. 
NOTE: 
Forms of condensation may also be classified on the basis of their location, 
i.e. at or near the earth’s surface and in free air. 
Dew, white frost, fog and mist come in the first category, whereas clouds 
are in the second category. 
 
DEW 
 
 When the moisture is deposited in the form of water droplets on cooler 
surfaces of solid objects such as stones, grass blades and plant leaves, it is 
known as dew.  
At night, various objects such as leaves etc. may frequently become cooler 
that the air above it.  
 
This causes water vapour contained In the air to get condensed and deposit 
on the cooled surface. This is known as dew. 
The ideal conditions for its formation are clear sky, calm air, high relative 
humidity, and cold and long nights. 
On cloudy nights cooling of the surface is not complete due to the 
greenhouse effect of the clouds and dew is not likely to be formed. 
 For the formation of dew, it is necessary that the dew point is above the 
freezing point 
 
FROST 
 
 
 Frost forms on cold surfaces when condensation takes place below freezing 
point (00C), i.e. the dew point is at or below the freezing point.  
The excess moisture is deposited in the form of minute ice crystals instead 
of water droplets. 
 The ideal conditions for the formation of white frost are the same as those 
for the formation of dew, except that the air temperature must be at or 
below the freezing point. 
In winter season the cooling of the surface may cause the ground 
temperature to fall below the freezing point.  
Page 3


 
WATER IN THE ATMOSPHERE – PART - 2 
FORMS OF CONDENSATION 
The forms of condensation can be classified on the basis of temperature at 
which the dew point is reached. 
Condensation can take place when the dew point is 
? lower than the freezing point, 
? higher than the freezing point. 
White frost, snow and some clouds (cirrus clouds) are produced when the 
temperature is lower than the freezing point. 
Dew, fog and clouds result even when the temperature is higher than the 
freezing point. 
NOTE: 
Forms of condensation may also be classified on the basis of their location, 
i.e. at or near the earth’s surface and in free air. 
Dew, white frost, fog and mist come in the first category, whereas clouds 
are in the second category. 
 
DEW 
 
 When the moisture is deposited in the form of water droplets on cooler 
surfaces of solid objects such as stones, grass blades and plant leaves, it is 
known as dew.  
At night, various objects such as leaves etc. may frequently become cooler 
that the air above it.  
 
This causes water vapour contained In the air to get condensed and deposit 
on the cooled surface. This is known as dew. 
The ideal conditions for its formation are clear sky, calm air, high relative 
humidity, and cold and long nights. 
On cloudy nights cooling of the surface is not complete due to the 
greenhouse effect of the clouds and dew is not likely to be formed. 
 For the formation of dew, it is necessary that the dew point is above the 
freezing point 
 
FROST 
 
 
 Frost forms on cold surfaces when condensation takes place below freezing 
point (00C), i.e. the dew point is at or below the freezing point.  
The excess moisture is deposited in the form of minute ice crystals instead 
of water droplets. 
 The ideal conditions for the formation of white frost are the same as those 
for the formation of dew, except that the air temperature must be at or 
below the freezing point. 
In winter season the cooling of the surface may cause the ground 
temperature to fall below the freezing point.  
 
In such a situation the moisture contained in air condenses and freezes on 
various objects on the ground making a thin layer of ice. This is called 
Frost. 
SMOG  
Smog = smoke + fog caused by the burning of large amounts of coal, 
vehicular emission and industrial fumes . 
Smog is also called smoke fog. Smog is a combination of water particles 
and fine particles of carbon and other substances contained In smoke. 
FOG AND MIST 
 
 
When the temperature of an air mass containing a large quantity of water 
vapour falls all of a sudden, condensation takes place within itself on fine 
dust particles.  
Fogs are mini clouds in which condensation takes place around nuclei 
provided by the dust, smoke, and the salt particles. 
So, the fog is a cloud with its base at or very near to the ground. 
 In urban and industrial centres smoke provides plenty of nuclei which help 
the formation of fog and mist.  
Such a condition when fog is mixed with smoke, is described as smog.  
The only difference between the mist and fog is that mist contains more 
moisture than the fog.  
In mist each nuceli contains a thicker layer of moisture.  
Page 4


 
WATER IN THE ATMOSPHERE – PART - 2 
FORMS OF CONDENSATION 
The forms of condensation can be classified on the basis of temperature at 
which the dew point is reached. 
Condensation can take place when the dew point is 
? lower than the freezing point, 
? higher than the freezing point. 
White frost, snow and some clouds (cirrus clouds) are produced when the 
temperature is lower than the freezing point. 
Dew, fog and clouds result even when the temperature is higher than the 
freezing point. 
NOTE: 
Forms of condensation may also be classified on the basis of their location, 
i.e. at or near the earth’s surface and in free air. 
Dew, white frost, fog and mist come in the first category, whereas clouds 
are in the second category. 
 
DEW 
 
 When the moisture is deposited in the form of water droplets on cooler 
surfaces of solid objects such as stones, grass blades and plant leaves, it is 
known as dew.  
At night, various objects such as leaves etc. may frequently become cooler 
that the air above it.  
 
This causes water vapour contained In the air to get condensed and deposit 
on the cooled surface. This is known as dew. 
The ideal conditions for its formation are clear sky, calm air, high relative 
humidity, and cold and long nights. 
On cloudy nights cooling of the surface is not complete due to the 
greenhouse effect of the clouds and dew is not likely to be formed. 
 For the formation of dew, it is necessary that the dew point is above the 
freezing point 
 
FROST 
 
 
 Frost forms on cold surfaces when condensation takes place below freezing 
point (00C), i.e. the dew point is at or below the freezing point.  
The excess moisture is deposited in the form of minute ice crystals instead 
of water droplets. 
 The ideal conditions for the formation of white frost are the same as those 
for the formation of dew, except that the air temperature must be at or 
below the freezing point. 
In winter season the cooling of the surface may cause the ground 
temperature to fall below the freezing point.  
 
In such a situation the moisture contained in air condenses and freezes on 
various objects on the ground making a thin layer of ice. This is called 
Frost. 
SMOG  
Smog = smoke + fog caused by the burning of large amounts of coal, 
vehicular emission and industrial fumes . 
Smog is also called smoke fog. Smog is a combination of water particles 
and fine particles of carbon and other substances contained In smoke. 
FOG AND MIST 
 
 
When the temperature of an air mass containing a large quantity of water 
vapour falls all of a sudden, condensation takes place within itself on fine 
dust particles.  
Fogs are mini clouds in which condensation takes place around nuclei 
provided by the dust, smoke, and the salt particles. 
So, the fog is a cloud with its base at or very near to the ground. 
 In urban and industrial centres smoke provides plenty of nuclei which help 
the formation of fog and mist.  
Such a condition when fog is mixed with smoke, is described as smog.  
The only difference between the mist and fog is that mist contains more 
moisture than the fog.  
In mist each nuceli contains a thicker layer of moisture.  
 
Mists are frequent over mountains as the rising warm air up the slopes 
meets a cold surface.  
Fogs are drier than mist and they are prevalent where warm currents of air 
come in contact with cold currents.  
 
HAZE  
 
Haze is traditionally an atmospheric phenomenon in which dust, smoke, 
and other dry particulates obscure the clarity of the sky. 
CLOUDS 
Cloud is a mass of minute water droplets or tiny crystals of ice formed by 
the condensation of the water vapour in free air at considerable elevations.